Wheel drive unit

ABSTRACT

A wheel drive unit comprises a bearing unit for wheel drive which is light in weight and low in cost. The components constituting the bearing unit for wheel drive have optimum properties to secure the durability thereof. Of the components constituting the bearing unit for wheel drive, the portions indicated by a diagonal grid hatching are quench-hardened with the other portions being not quench-hardened and left as they are, whereby the rolling fatigue life and wear-resistance of the components are improved and cracking is prevented.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. application Ser. No. 09/931,653 filed Aug.16, 2001, now abandoned, which is a continuation under 35 U.S.C. §120 ofInternational Application PCT/JP01/07045, filed Aug. 15, 2001.

FIELD OF THE INVENTION

The present invention relates to a wheel drive unit which is acombination of a wheel support rolling bearing unit, a constant velocityjoint unit and a snap ring, and is used for rotatably supporting withrespect to a suspension unit, a driven wheel {the front wheel of a FFvehicle (front engine, front drive wheel) the rear wheel of both a FRvehicle (front engine, rear drive wheel) and a RR vehicle (rear engine,rear drive wheel) and all wheels of a 4WD vehicle (four drive wheel)}supported on an independent suspension type suspension, and forrotationally driving the driven wheel.

BACKGROUND OF THE INVENTION

In order to rotatably support a vehicle wheel with respect to asuspension unit, various kinds of rolling bearing units for wheelsupport with an outer ring and inner ring assembled so as to be freelyrotatable via rolling elements, are used. Moreover, a wheel supportrolling bearing unit for supporting a driven wheel in a suspension ofthe independent suspension type and rotationally driving the drivenwheel, must be combined with a constant velocity joint to smoothlytransmit (maintain constant velocity) the rotation of the drive shaft tothe abovementioned vehicle wheel, regardless of the relativedisplacement between a differential gear and the driven wheel and of asteering angle applied to the wheel. FIG. 6 shows a typical bearing unit3 for wheel drive wherein a rolling bearing unit 1 for wheel support anda constant velocity joint 2 are combined together for this kind ofpurpose.

This rolling bearing unit for wheel support 1 is formed by rotatablysupporting a hub 5 and an inner ring 6 on the inner diameter side of anouter ring 4 via a plurality of rolling elements 7. Of these, the outerring 4 when connectingly secured to a knuckle 9 (refer to FIG. 7mentioned below) constituting a suspension unit by means of a firstflange 8 provided on the outer peripheral face thereof, does not rotateeven at the time of use. Furthermore, a double row of outer ringraceways 10 is provided on the inner peripheral face of the outer ring4, and the hub 5 and the inner ring 6 are rotatably supported on theinner diameter side, concentric with the outer ring 4.

Of these, the hub 5 is provided with a second flange 11 for supportingthe wheel, on a portion near an outer end (the end which is on theoutside in a widthwise direction of the vehicle when fitted to thevehicle, namely, the left hand side of each figure including FIG. 6) ofthe outer peripheral face. Furthermore, the first inner ring raceway 12is formed on a central portion of the outer peripheral face of the hub5. Similarly, an inner ring 6 with a second inner ring raceway 14 formedon an outer peripheral face thereof, is externally secured to a smalldiameter step 13 formed on an inner end (the end which is on the middleside in a widthwise direction of the vehicle when fitted to the vehicle,namely the right hand side of each figure.). Moreover, in the centerportion of the hub 5, a spline bore 15 is provided, so that the hub 5 isformed in a hollow cylindrical shape.

On the other hand, the constant velocity joint 2 has an outer ring 16for constant velocity joint, an inner ring 17 for constant velocityjoint and a spline shaft 18. Of these, the outer ring 16 for constantvelocity joint and the spline shaft 18 constitute a drive member 19.That is, the spline shaft 18 is provided on an outer end of the drivemember 19 and is freely engaged with the spline bore 15, and the outerring 16 for constant velocity joint is provided on an inner end of thedrive member 19. At a plurality of places on the inner peripheral faceof the outer ring 16 for constant velocity joint around thecircumferential direction are respectively formed outside engaginggrooves 20 at right angles to the circumferential direction. Moreover,regarding the inner ring 17 for constant velocity joint, a second splinebore 21 is formed at right angles to the circumferential direction in acenter portion, and on the outer peripheral face, inside engaginggrooves 22 are formed at right angles to the circumferential directionin portions coinciding with the outside engaging grooves 20. Moreover,balls 23 are provided between each of the inside engaging grooves 22 andeach of the outside engaging grooves 20 so as to be freely rotatablealong each engaging groove 22 and 20, with the balls 23 being retainedin a cage 24. At a part of the inner peripheral face of the outer ring16 for constant velocity joint, portions between pairs ofcircumferentially adjacent outside engaging grooves 20 constitute cageguide faces 25. Each cage guide face 25 is positioned on a singlespherical surface with a displacement center of the constant velocityjoint 2 as the center thereof. Regarding the shape of the constituentelements of this kind of constant velocity joint 2, this is similar tothe case of a well know Rzeppa type or Birfield type constant velocityjoint, and since this has no relevance to the gist of the presentinvention, detailed description is omitted.

In combining the above described constant velocity joint 2 and the wheelsupport rolling bearing unit 1, the spline shaft 18 is inserted into thespline bore 15 of the hub 5 from the inner side towards the outer side.Then a nut 27 is screwed onto an external thread portion 26 provided onan outer end portion of the spline shaft 18 projecting from an outer endface of the hub 5, and then by tightening, these are connected andsecured together. In this condition, since the inner end face of theinner ring 6 is abutted against the outer end face of the outer ring 16for constant velocity joint, there is no displacement of the inner ring6 in a direction to come off from the small diameter step portion 13. Atthe same time, an appropriate pre-load is applied to each of the rollingelements 7.

Moreover, when fitted to the suspension unit of a vehicle, a male splineportion 29 provided on an outer end of a drive shaft 28 is splineengaged with a second spline bore 21 provided in a central portion ofthe inner ring 17 for constant velocity joint. Then, a snap ring 37which is stoppingly engaged in an engaging groove 30 formed around thewhole periphery in the outer peripheral face at the outer end of themale spline portion 29, is engaged with an engaging step portion 32formed in an opening rim at the outer end of the second spline bore 21,thereby preventing the male spline portion 29 from coming out from thesecond spline bore 21. Furthermore, the inner end of the drive shaft 28is connectingly secured to the center of a trunnion 34 (refer to FIG. 1showing a first example of an embodiment of the present invention) of atripod type constant velocity joint 33 provided on an output shaft of adifferential gear.

Regarding the first example of the abovementioned conventionalconstruction shown in FIG. 6, the weight is increased because therolling bearing unit 1 for wheel support and the constant velocity joint2 are connectingly secured based on the threaded and tightenedengagement between the male thread portion 29 and the nut 27. That is,providing the external thread portion 26 on the spline shaft 18 of theconstant velocity joint 2 requires lengthening of the spline shaft 18,and the nut 27 also becomes necessary. Therefore the axial dimension andthe weight of the bearing unit 3 for wheel drive are increased by themale thread portion 26 and the nut 27.

To address this problem, in the specification of U.S. Pat. No. 4,881,842is disclosed as shown in FIG. 7, a bearing unit 3 a for wheel drive thatenables shortening of the axial dimension and a reduction in weight, byconnectingly securing the rolling bearing unit for wheel support and theconstant velocity joint by a relatively simple construction. Also in thecase of the second example of the conventional construction shown inFIG. 7, a hub 5 is rotatably supported on the inside of an outer ring 4secured to a knuckle 9, by rolling elements 7 arranged in a double row.Moreover, a spline shaft 18 of a drive member 19 a is spline engagedwith a spline bore 15 formed in a central portion of the hub 5. Anengaging portion 35 is formed in an outer end surface of the splineshaft 18 for engaging with a tool for drawing the spline shaft 18 intothe spline bore 15.

Furthermore, the spline shaft 18 is prevented from coming off from thehub 5 by a snap ring 31 which is stoppingly engaged in an engaginggroove 36 formed in an outer peripheral face of the spline shaft 18 at aportion close to its tip end (outer end). In this condition, resilientring 60 is resiliently compressed between the hub 5 and the outer ring16 for constant velocity joint of the drive member 19 a, therebyeffecting play prevention of the spline shaft 18 and the hub 5. In thecase of the second example of this kind of conventional construction, tothe extent that connection of the rolling bearing unit 1 a for wheelsupport and the constant velocity joint 2 a is performed by the snapring 31, an overall smaller size and lighter weight for the bearing unit3 a for wheel drive is achieved.

Moreover, in Japanese Patent Publication No. Tokukai Hei 10-264605disclosed a bearing unit 3 b for wheel drive such as shown in FIG. 8. Arolling bearing unit 1 b for wheel support constituting the bearing unit3 b for wheel drive has a hollow hub 5 a such that a constant velocityjoint outer ring 16 a constituting a constant velocity joint 2 bcorresponding to the drive member described in the claims, is connectedto an inner end of the hollow hub 5 a via a spacer 38. Of the inner andouter peripheral surfaces of this spacer 38 formed in a shortcylindrical shape, an inner diameter side female spline portion 39 isformed on the inner peripheral surface of the spacer 38, and an outerdiameter side male spline portion 40 corresponding to the first splineportion described in the claims is formed on the outer peripheralsurface of the spacer 38. This spacer 38 is assembled on an outerperipheral face at the inner end of the hub 5 a, with an inner diameterside male spline portion 41 formed on an outer peripheral surfacethereof in spline engagement without play with the inner diameter sidefemale spline portion 39. Then, in this condition, an inner end face ofthe spacer 38 is clamped by a crimped portion 42 formed on the inner endof the hub 5 a, so that the spacer 38 is secured without play to theinner end of the hub 5 a. Moreover, in Japanese Patent Publication No.Tokukai Hei 10-264605 is also disclosed a construction where the innerring and the spacer are formed as one body.

On the other hand, an outer diameter side female spline portion 43corresponding to the second spline portion described in the claims,which is formed on the inner peripheral face at the outer end of theouter ring 16 a for constant velocity joint is spline engaged with anouter diameter side male spline portion 40. That is, the outer diameterside female spline portion 43 is formed in an inner peripheral face atthe outer end of the outer ring 16 a for constant velocity joint.Moreover, as mentioned above, the outer diameter side female splineportion 43 is spline engaged with the outer diameter side male splineportion 40 formed on the outer peripheral surface of the spacer 38.

A snap ring 31 a spans between the outer diameter side female splineportion 43 and the outer diameter side male spline portion 40 which arespline engaged with each other as described above, so that the outerring 16 a for constant velocity joint cannot separate from the spacer38. That is, the snap ring 31 a is formed in a semi-circle annular shapeand made to span between an inside engaging groove 44 corresponding to afirst connecting portion, which is formed around the whole periphery inthe outer peripheral surface of the spacer 38, and an outside engaginggroove 45 corresponding to a second connecting portion described in theclaims, which is formed around the whole periphery in the innerperipheral surface at the outer end of the outer ring 16 a for constantvelocity joint. Hence the outer ring 16 a for constant velocity jointand the spacer 38 cannot be displaced from each other in the axialdirection.

The construction of the connecting portion of the hub 5 a and the outerring 16 a for constant velocity joint is as mentioned above, and thishub 5 a is rotatably supported on the inner diameter side of the outerring 4 by a double row angular type ball bearing. An inner ring 6constituting this ball bearing is clampingly secured between an outerend face of the spacer 38 and a step face 46 existing on the outer endof a small diameter step portion 13 formed on an outer peripheral faceat the central portion of the hub 5 a.

In the case of the bearing unit 3 b for wheel drive described inJapanese Patent Publication No. Tokukai Hei 10-264605 as describedabove, the spline shaft 18 can be omitted from the second example of theconventional construction shown in FIG. 7, and to that extent, the costand weight can be further reduced.

In the case of the second and third examples of the conventionalconstruction shown in FIG. 7 and FIG. 8, in comparison to the case ofthe first example of the conventional construction shown in FIG. 6, areduction of cost and weight is effected. However, in order tosufficiently maintain the durability of each constituent element, it isnecessary to optimize the properties of each constituent element. Thatis, at the time of using the wheel drive unit, various kinds of stresssuch as, force in the compression direction, force of the bendingdirection, and force in the tension direction and the like, are appliedto each constituent element of the rolling bearing unit for wheelsupport and the constant velocity joint which are combined together toform the wheel drive unit. However with regards to this point,heretofore no consideration has been given to make the properties ofeach constituent element optimum to deal with these stresses.

DISCLOSURE OF THE INVENTION

The present invention was invented taking this situation intoconsideration, in order to optimize the properties of each constituentelement so as to ensure durability of the wheel drive unit.

The present invention provides a wheel drive unit comprising a rollingbearing unit for vehicle wheel, a constant velocity joint unit and asnap ring. The constant velocity joint unit comprises a first constantvelocity joint having an output portion and a input portion connected toan output portion of a differential gear. A transmission shaft having anoutput end and an input end is connected to the output portion of thefirst constant velocity joint A second constant velocity joint having anoutput portion and an input portion is connected to the output end ofthe transmission shaft. The rolling bearing unit for vehicle wheelcomprises an outer ring having an inner peripheral surface formed withouter ring raceways and being not rotatable during use, a hollow hubhaving an outer peripheral surface formed with an flange for supportinga vehicle wheel near the outer end thereof, with a first inner ringraceway at the middle portion thereof, and with a small diameter steppedportion formed near the inner end thereof. An inner ring having an outerperipheral surface is formed with a second inner ring raceway and fittedonto the small diameter stepped portion of the hub, the hub having theinner end plastically deformed radially outward to form a crimpedportion to prevent the inner ring from coming out of the smallerdiameter portion. A plurality of rolling members are rotatably providedbetween each of the outer ring raceways and the first and second innerring raceways, and a first spline portion is provided on a peripheralsurface portion of the hub or a member securely connected to the hub.

The second constant velocity joint comprises a drive member having aperipheral surface at the outer end thereof formed with a second splineportion in spline engagement relation with the first spline portion, andan outer ring for constant velocity joint at the inner end thereof toconstitute the second constant velocity joint. A first engagementportion is provided on a peripheral surface portion of the hub or amember securely connected to the hub. A second engagement portion isprovided on the peripheral surface at the outer end of the drive member.The snap ring spans between the first engagement portion and the secondengagement portion to prevent disengagement between the first splinesection and the smaller diameter stepped portion of the hub has astepped face portion at the innermost end thereof. The inner ring has aninner end face abutted to the stepped surface portion. On the outerperipheral surface of the hub, at least the first inner ring raceway andthe stepped surface portion is quench-hardened, while on the innerperipheral surface of the hub, at least a portion located on the innerdiameter side of the quench-hardened stepped surface portion; and thecrimped portion is not quench-hardened. At least one of the hub or themember securely connected to the hub and the drive member has aperipheral portion formed with an engagement groove for the first andsecond engagement portions and not quench-hardened. The outer ring forconstant velocity joint is formed with outside engagement grooveportions on the inner peripheral surface thereof with cage guideportions each existing between a circumferentially adjacent pair of thecage guide portions, and on the inner peripheral surface of the outerring for constant velocity joint, at least the outside engagement grooveportions and the cage guide portions is quench-hardened.

The wheel drive unit of the present invention comprises a rollingbearing unit for wheel support, a constant velocity joint unit and asnap ring.

Of these, the constant velocity joint unit has a first constant velocityjoint for connecting an input portion thereof to an output portion of adifferential gear, a transmission shaft with an input side end portionthereof connected to an output portion of the first constant velocityjoint, and a second constant velocity joint with an input portionthereof to an output side end portion of the transmission shaftconnected.

Furthermore, the rolling bearing unit for wheel support has an outerring, a hollow hub, rolling elements and a first spline portion.

Of these, the outer ring has a double row of outer ring raceways on aninner peripheral face thereof and does not rotate at the time of use.

Moreover, the hub is provided with a flange for supporting a vehiclewheel, on a part near an outer end of an outer peripheral face thereof,and a first inner ring raceway on a central portion thereof. An innerring with a second inner ring raceway formed on an outer peripheral facethereof is externally secured to a small diameter step portion formed ona part of the outer peripheral face near the inner end thereof, and thecoming off of the inner ring from the small diameter step portion isprevented by a crimped portion formed by plastic deformation of theinner end portion in a radially outward direction.

Furthermore, the rolling elements are respectively provided severally soas to be freely rotatable between each of the outer ring raceways andeach of the first and second inner ring raceways.

Moreover, the first spline portion is provided on the hub or on a partof a peripheral face of a member connectingly secured to the hub.

In addition, the second constant velocity joint incorporates a drivemember with a second spline portion for spline engagement with the firstspine portion provided on an outer end peripheral face thereof, and aninner end portion serving as a constant velocity joint outer ringconstituting the second constant velocity joint.

Moreover, in a condition with the first spline portion and the secondspline portion spline connected to each other, the snap ring spansbetween a first engaging portion provided on the hub or a part of theperiphery of a member connectingly secured to the hub, and a secondengaging portion provided on a peripheral face at the outer end of thedrive member, thereby preventing the separation of the connectionbetween the first spline portion and the second spline portion.

Furthermore, of the outer peripheral face of the hub, at least the firstinner ring raceway portion and the stepped face portion existing at theinnermost end of the small diameter step portion which abuts with theouter end face of the inner ring, are quench-hardened. Furthermore, atleast a portion of the inner peripheral face of the hub, positioned onthe inner diameter side of the portion that is quench-hardenedcorresponding to the small diameter step portion, and the portion forforming the crimped portion are not quench-hardened. Moreover, at leastone portion of the peripheral face of at least one of the hub or amember connectingly secured to the hub, and the drive mentor, which isformed with the engaging groove for serving as the first connectingportion or the second connecting portion, is not quench-hardened. Inaddition, of the inner peripheral face of the outer ring for constantvelocity joint, at least the outside engaging groove portion and thecage guide face portion existing between each of the circumferentiallyadjacent outside engaging groove pairs are quench-hardened.

According to the wheel drive unit of the present invention constructedas described above, because the properties of each constituent elementcan be such as to correspond optimally to the stress etc. applied toeach member, the durability can be sufficiently ensured.

Firstly, of the outer peripheral face of the hub, because the firstinner ring raceway portion is quench-hardened, the rolling fatigue lifeof this first inner ring raceway portion is improved. Furthermore,because the stepped face portion existing at the innermost end of thesmall diameter step portion is quench-hardened, the thrust load whichthis stepped face portion bears can be made sufficiently large.Accordingly, when the crimped portion is formed on the inner end portionof the hub in a condition with the outer end face of the inner ringabutted against the stepped face portion, so that the inner ring issecured to the hub, there is no plastic deformation of the stepped faceportion. As a result, by clamping the inner ring with the crimpedportion an appropriate pre-load can be applied to each rolling element.

Furthermore, at least a part of the inner peripheral face of the hub,positioned on the inner diameter side of the quench-hardened portioncorresponding to the small diameter step portion, is notquench-hardened, and therefore there is no quench-hardened portionpenetrating from the inner peripheral face of the hub to the outerperipheral face thereof. Therefore, the existence of a partially brittleportion in the hub is prevented. Hence damage such as cracking occurringin the hub during the process of quench-hardening of the hub, orlowering of the shock resistance of the hub can be prevented.

Furthermore, because the portion of the hub to be crimped is notquench-hardened, when forming the crimped portion in order toconnectingly secure the inner ring to the hub, damage such as crackingdoes not occur at this crimped portion, and a high quality crimpedportion can thus be formed. Furthermore, at one portion of theperipheral face of at least one of the hub or a member connectinglysecured to the hub, and the drive member, which is formed with theengaging groove being the first connecting portion or the secondconnecting portion, is not quench-hardened. Therefore, damage such ascracking due to heat treatment does not occur in the portion where theabovementioned engaging groove is formed and where distortion can easilyoccur with heat treatment.

Moreover, of the inner peripheral face of the outer ring for constantvelocity joint, the rolling fatigue life of the outer engaging grooveportion is improved with the quench-hardening of the outer engaginggroove portion. Furthermore, of the inner peripheral face of the outerring for constant velocity joint, since the cage guide face portionexisting between the circumferentially adjacent outer engaging groovepairs is quench-hardened, the wear resistance and seizure resistance ofthe cage guide face portion which rubbingly contacts with the outerperipheral face of the cage constituting the constant velocity joint canbe improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view to show a first example of theembodiment of the present invention.

FIG. 2 is a partly cut-away cross sectional view to show a left part ofFIG. 1.

FIG. 3 is an enlarged view of Portion III of FIG. 2.

FIG. 4 is a cross sectional view to show a second example of theembodiment of the present invention.

FIG. 5 is a cross sectional view to show a third example of theembodiment of the present invention.

FIG. 6 is a cross sectional view to show a first example of theconventional structure.

FIG. 7 is a cross sectional view to show a second example of theconventional structure.

FIG. 8 is a cross sectional view to show a third example of theconventional structure.

FIG. 9 is a cross-sectional view of an alternative embodiment of thepresent invention shown in FIG. 5.

SUMMARY OF THE INVENTION

The wheel drive unit of the present invention comprises a rollingbearing unit for wheel support, a constant velocity joint unit and asnap ring.

Of these, the constant velocity joint unit has a first constant velocityjoint for connecting an input portion thereof to an output portion of adifferential gear, a transmission shaft with an input side end portionthereof connected to an output portion of the first constant velocityjoint, and a second constant velocity joint with an input portionthereof to an output side end portion of the transmission shaftconnected.

Furthermore, the rolling bearing unit for wheel support has an outerring, a hollow hub, rolling elements and a first spline portion.

Of these, the outer ring has a double row of outer ring raceways on aninner peripheral face thereof and does not rotate at the time of use.

Moreover, the hub is provided with a flange for supporting a vehiclewheel, on a part near an outer end of an outer peripheral face thereof,and a first inner ring raceway on a central portion thereof. An innerring with a second inner ring raceway formed on an outer peripheral facethereof is externally secured to a small diameter step portion formed ona part of the outer peripheral face near the inner end thereof, and thecoming off of the inner ring from the small diameter step portion isprevented by a crimped portion formed by plastic deformation of theinner end portion in a radially outward direction.

Furthermore, the rolling elements are respectively provided severally soas to be freely rotatable between each of the outer ring raceways andeach of the first and second inner ring raceways.

Moreover, the first spline portion is provided on the hub or on a partof a peripheral face of a member connectingly secured to the hub.

In addition, the second constant velocity joint incorporates a drivemember with a second spline portion for spline engagement with the firstspine portion provided on an outer end peripheral face thereof, and aninner end portion serving as a constant velocity joint outer ringconstituting the second constant velocity joint.

Moreover, in a condition with the first spline portion and the secondspline portion spline connected to each other, the snap ring spansbetween a first engaging portion provided on the hub or a part of theperiphery of a member connectingly secured to the hub, and a secondengaging portion provided on a peripheral face at the outer end of thedrive member, thereby preventing the separation of the connectionbetween the first spline portion and the second spline portion.

Furthermore, of the outer peripheral face of the hub, at least the firstinner ring raceway portion and the stepped face portion existing at theinnermost end of the small diameter step portion which abuts with theouter end face of the inner ring, are quench-hardened. Furthermore, atleast a portion of the inner peripheral face of the hub, positioned onthe inner diameter side of the portion that is quench-hardenedcorresponding to the small diameter step portion, and the portion forforming the crimped portion are not quench-hardened. Moreover, at leastone portion of the peripheral face of at least one of the hub or amember connectingly secured to the hub, and the drive member, which isformed with the engaging groove for serving as the first connectingportion or the second connecting portion, is not quench-hardened. Inaddition, of the inner peripheral face of the outer ring for constantvelocity joint, at least the outside engaging groove portion and thecage guide face portion existing between each of the circumferentiallyadjacent outside engaging groove pairs are quench-hardened.

According to the wheel drive unit of the present invention constructedas described above, because the properties of each constituent elementcan be such as to correspond optimally to the stress etc. applied toeach member, the durability can be sufficiently ensured.

Firstly, of the outer peripheral face of the hub, because the firstinner ring raceway portion is quench-hardened, the rolling fatigue lifeof this first inner ring raceway portion is improved. Furthermore,because the stepped face portion existing at the innermost end of thesmall diameter step portion is quench-hardened, the thrust load whichthis stepped face portion bears can be made sufficiently large.Accordingly, when the crimped portion is formed on the inner end portionof the hub in a condition with the outer end face of the inner ringabutted against the stepped face portion, so that the inner ring issecured to the hub, there is no plastic deformation of the stepped faceportion. As a result, by clamping the inner ring with the crimpedportion an appropriate pre-load can be applied to each rolling element.

Furthermore, at least a part of the inner peripheral face of the hub,positioned on the inner diameter side of the quench-hardened portioncorresponding to the small diameter step portion, is notquench-hardened, and therefore there is no quench-hardened portionpenetrating from the inner peripheral face of the hub to the outerperipheral face thereof. Therefore, the existence of a partially brittleportion in the hub is prevented. Hence damage such as cracking occurringin the hub during the process of quench-hardening of the hub, orlowering of the shock resistance of the hub can be prevented.

Furthermore, because the portion of the hub to be crimped is notquench-hardened, when forming the crimped portion in order toconnectingly secure the inner ring to the hub, damage such as crackingdoes not occur at this crimped portion, and a high quality crimpedportion can thus be formed. Furthermore, at one portion of theperipheral face of at least one of the hub or a member connectinglysecured to the hub, and the drive member, which is formed with theengaging groove being the first connecting portion or the secondconnecting portion, is not quench-hardened. Therefore, damage such ascracking due to heat treatment does not occur in the portion where theabovementioned engaging groove is formed and where distortion can easilyoccur with heat treatment.

Moreover, of the inner peripheral face of the outer ring for constantvelocity joint, the rolling fatigue life of the outer engaging grooveportion is improved with the quench-hardening of the outer engaginggroove portion. Furthermore, of the inner peripheral face of the outerring for constant velocity joint, since the cage guide face portionexisting between the circumferentially adjacent outer engaging groovepairs is quench-hardened, the wear resistance and seizure resistance ofthe cage guide face portion which rubbingly contacts with the outerperipheral face of the cage constituting the constant velocity joint canbe improved.

Now, the present invention is further explained referring to theattached drawings.

Description of the Best Embodiment for Working the Invention

FIG. 1 to FIG. 3 show a first example of an embodiment of the presentinvention corresponding to claims of the invention. A characteristic ofthe present invention is the point that with a construction enablingeasy connection of a rolling bearing unit 1 c for wheel supportconstituting a drive unit for vehicle wheel, to a constant velocityjoint 2 c, being a second constant velocity joint described in theclaims, the reliability and durability of the rolling bearing unit 1 cfor wheel support and the constant velocity joint 2 c is ensured. Partof the basic construction of a bearing unit for wheel drive formed bycombining the rolling bearing unit 1 c for wheel support and theconstant velocity joint 2 c has many portions common to some of theconventional constructions shown in the FIG. 6 to FIG. 8. Therefore,equivalent portions are denoted by the like reference symbols, andrepeated explanation is omitted or made briefly. Hereunder is adescription centered on the different points between the characteristicportions of the present invention and those of the aforementionedconventional construction.

A hub 5 b constituting the rolling bearing unit 1 c for wheel support,is prepared to an approximate shape by hot forging a material such asS53CG, and is then processed to a desired shape and properties bysubjecting to machining, induction hardening, grinding andsuperfinishing. Of this, regarding the part subjected to inductionhardening, this will be explained in detail later, but of the surface ofthe hub 5 b, the surface hardness of the portion subjected to thisinduction hardening is H_(R)C 58˜64, and the effective thickness of thehardened layer is around 1.5˜3 mm.

An inner ring 6 formed with a second inner ring raceway 14 on an outerperipheral face thereof, is externally fitted to a small diameter stepportion 13 formed on a portion near the inner end of the hub 5 b formedas mentioned above. This inner ring 6 is prepared to an approximateshape by hot forging a material such as SUJ2, and then processed to adesired shape and properties by subjecting to machining, dip quenching,grinding and superfinishing. The hardness is H_(R)C60-64. Then, in orderto prevent the inner ring 6 formed as mentioned above from coming offfrom the abovementioned small diameter step portion 13, a crimpedportion 42 a is formed on an inner end portion of the hub 5 b. That is,after the inner ring 6 is externally fitted to the small diameter stepportion 13, the portion at the inner end of the hub 5 b projected fromthe inner end face of this inner ring 6 is plastically deformed radiallyoutward to form the crimped portion 42 a, and the inner end face of theinner ring 6 is thus retained by this crimped portion 42 a.

Furthermore, an engaging groove 47 corresponding to the secondconnecting portion described in the claims, is formed around the entireperiphery in the outer peripheral face at the outer end of the splineshaft 18 constituting the drive member 19 b incorporated into theconstant velocity joint 2 c. The drive member 19 b including the splineshaft 18 is prepared to an approximate shape by hot forging a materialsuch as S55CG, and is then processed to a desired shape and propertiesby subjecting to machining, induction hardening, grinding andsuperfinishing. Of this, regarding the part subjected to inductionhardening, this will be explained in detail later, but of the drivemember 19 b, the surface hardness of the portion subjected to thisinduction hardening is H_(R)C 58˜64. Regarding the effective thicknessof the hardened layer, this differs depending on location, but is around2˜7.5 mm. For example, regarding the inner peripheral face portion ofthe outer ring 16 b for constant velocity joint, because this issubjected to grinding after the quench-hardening, the thickness isaround 2˜4 mm. On the other hand, the outer peripheral face portion ofthe spline shaft 18 is not subjected to grinding and hence has athickness of around 5˜7.5 mm.

In the condition with the spline shaft 18 inserted into the spline bore15 provided in the center of the hub 5 b to thus constitute the bearingunit 3 c for wheel drive, the half on the outer diameter side of a snapring 31 b is engaged with the engaging step portion 32 a correspondingto the first engaging portion described in the claims, formed on aportion of the inner peripheral face near the outer end of the hub 5 b,while the half on the inner diameter side thereof stoppingly engaged inthe engaging groove 47, thereby preventing the spline shaft 18 fromcoming out from the spline bore 15. The snap ring 31 b is formed bybending into a semi-circle annular shape a material with a circularcross-section such as SWPA and SWPB, and in a free state has resiliencein the direction for expanding the diameter. Moreover, the hardness isH_(R)C 48-54.

The dimensions of this snap ring 31 b are, as mentioned below, fixed bydesign so that the allowable stress is not exceeded when passing throughthe spline bore 15 in order to assemble the bearing unit 3 c for wheeldrive, and at the time of use. In this case, if the spline module isfixed, the diameter of the cross-section of the snap ring 31 b can beincreased as the pitch circle diameter of the spline is increased. Forexample, in general use, in the case where an involute tooth profilewith the module being 1 and the pressure angle being 45 degrees, isconsidered, when the pitch circle diameter is 24 mm, the diameter of thecross-section is made 1.4 mm. Similarly when the pitch circle diameteris 30 mm, the diameter of the cross-section is made 1.7 mm. Furthermore,also regarding the dimensions of the installation portion for the snapring 31 b, this is fixed by design to correspond to the diameter of thecross-section of the snap ring 31 b. FIG. 3 shows one example of thedimensions of the installation portion for the case where the diameterof this cross-section is 1.7 mm. In the case where the pitch circlediameter is 30 mm, the diameter of the cross-section is not limited to1.7 mm, and can be appropriately set within a range of for example1.7˜2.5 mm.

Further, in the central bore of the hub 5 b, the part nearer the outerend opening than the engaging step portion 32 a is formed with no femalespline teeth and with a simple cylindrical surface. That is, the centralbore of the hub 5 b is divided into the spline bore 15 and a simplecircular bore 48 with a larger diameter than the spline bore 15, withthe engaging step portion 32 a as a the border therebetween.Furthermore, the snap ring 31 b is fitted into the engaging groove 47prior to insertion of the spline shaft 18 into the spline bore 15. Whenthe spline shaft 18 is inserted into the spline bore 15, the snap ring31 b passes through inside the spline bore 15 with the diameterresiliently contracted. Then, in the condition with the snap ring 31 bmatching with the engaging step portion 32 a, the diameter thereof isresiliently restored, and similarly to above, the snap ring 31 b isspanned between the engaging step portion 32 a and the engaging groove47.

Furthermore, an opening portion on the outer end side of the centralbore of the hub 5 b is covered by a cap 49. On the other hand, a sealring 51 is externally fitted to an outer peripheral face of a shoulder50 formed on a base end of the outer ring 16 b for constant velocityjoint constituting the drive member 19 b. This seal ring 51, in acondition externally secured to the shoulder 50, is resilientlycompressed between the inside face of the crimped portion 42 a and theoutside face of the outer ring 16 b for constant velocity joint, thusclosing off a gap between the crimped portion 42 a and the outer ring 16b for constant velocity joint.

In this manner, in the case shown in the figure, foreign matter such asmuddy water is prevented from entering into the spline engaging portion52 between the spline shaft 18 and the spline bore 15, by the cap 49 andthe seal ring 51, thus preventing rusting of the spline engaging portion52. Further, in the example shown in the figure, the outside face of theshoulder 50 and the part near the inner diameter of the inside face ofthe crimped portion 42 a face each other via the gap 53. In the casewhere a large thrust load is applied between the hub 5 b and the drivemember 19 b in a direction to make the hub 5 b and the outer ring 16 bfor constant velocity joint approach each other, the gap 53 is lost, andthe outside face of the shoulder 50 and the part near the inner diameterof the inside face of the crimped portion 42 a are abutted together. Inthis condition, the hub 5 b and the outer ring 16 b for constantvelocity joint cannot come any closer together. Therefore, the size ofthe gap 53 is appropriately constrained so that even with a large thrustload, the seal ring 51 is not excessively compressed. A proviso is thatthe interference of the seal lip of the seal ring 51 in a condition withthe size of the gap 53 a maximum, is greater than the settling amount ofthe seal ring 51 with use over a long period. The reason for this is inorder to maintain the resilient compression condition of the seal ring51 between the inside face of the crimped portion 42 a and the outer endface of the outer ring 16 b for constant velocity joint, even in thecase where the seal ring 51 has settled.

Of the bearing unit 3 c for wheel drive constructed as mentioned above,the portion shown by a diagonal grid hatching in FIG. 2 on a part of thesurface of the hub 5 b and drive member 19 b is quench-hardened byinduction quench-hardening. Firstly, of the outer peripheral face of thehub 5 b, the intermediate portion excluding the axially opposite ends isquench-hardened. Regarding the quench-hardened portion related to theouter peripheral face of this hub 5 b, describing from the outside, thebase end portion of the second flange 11 for supporting the wheel onthis hub 5 b is quench-hardened. This portion is hardened in order toimprove the bending rigidity of the second flange 11, and so that thesecond flange 11 does not bendingly deform in spite of the momentapplied from the vehicle wheel at the time of traveling, and at the sametime to suppress wear accompanying sliding of a seal lip constituting aseal ring 54 which is secured to the outer end of an outer ring 4.

Next, the portions of an first inner ring raceway 12 and a stepped face46 existing at the innermost end of the small diameter step portion 13and abutted against the outer end face of the inner ring 6 isquench-hardened. The portion of first inner ring raceway 12 isquench-hardened to improve the rolling fatigue life of the portion offirst inner ring raceway 12. Furthermore, the portion of the steppedface 46 existing at the innermost end of the small diameter step portion13 is quench-hardened to sufficiently increase the thrust load that thisportion of the stepped face 46 can bear. Consequently, in the conditionwith the outer end face of the inner ring 6 abutted against the steppedface 46, when the crimped portion 42 a is formed on the inner end of thehub 5 b to secure the inner ring 6 to the hub 5 b, the portion ofstepped face 46 cannot be plastically deformed. As a result, anappropriate pre-load is applied to each rolling element 7 by theclamping of the inner ring 6 with the crimped portion 42 a.

Furthermore, on the inner peripheral face of the hub 5 b, the engagingstep portion 32 a and the portion near the engaging step portion 32 a ishardened by induction quench-hardening. The induction quench-hardeningof these portions is performed in order to prevent plastic deformationin the case where the engaging step portion 32 a is strongly pressed bythe snap ring 31 b, and to reliably prevent the engagement between theengaging step portion 32 a and the snap ring 31 b from being separatedfrom each other. In the case of the present example, because theengaging step portion 32 a and the small diameter step portion 13 areseparated from each other, the quench-hardened layer of the portion ofengaging step portion 32 a and the quench-hardened layer of the portionof stepped face 46 are not connected to each other. Consequently, thequench-hardened layer does not penetrate through both the inner and theouter peripheral faces of the hub 5 b. Hence the shock resistance(tenacity) of the hub 5 b can be ensured. On the other hand, in the casewhere the engaging step portion provided on the inner peripheral face ofthe hub and the stepped face provided on the outer peripheral face areadjacent to each other, when the quench-hardened layer is formed in theengaging step portion, there is the possibility for the quench-hardenedlayer to penetrate through both the inner and outer peripheral faces ofthe hub. In such a case, it becomes difficult to ensure the shockresistance of the hub. Therefore, no quench-hardened layer is formed inthe engaging step portion (no quench-hardening is conducted).

Furthermore, regarding the drive member 19 b, the outer peripheral facefrom the base end to the middle portion of the spline shaft 18 isquench-hardened. Further, in the example shown in the figure, a portionof the outer end face abutted against the inner diameter side half ofthe seal ring 51 of the outer ring 16 b for constant velocity joint isalso quench-hardened. Of these, the base end of the spline shaft 18 isquench-hardened to ensure the fatigue strength of this base end withrespect to the bending moment repeatedly applied to the spline shaft 18at the time of traveling. Furthermore, the middle portion of the splineshaft 18 is quench-hardened to suppress plastic deformation and wear ofa male spline portion 29 a formed on the outer peripheral face of thespline shaft 18. Moreover, the outer end face of the outer ring 16 b forconstant velocity joint is quench-hardened to suppress deformation ofthe bearing face of the seal ring 51 and thus ensure the sealperformance due to the seal ring 51. Furthermore, in the example shownin the figure, because the outer end portion of the outer ring 16 b forconstant velocity joint is made thin in order to lighten the outer ring16 b for constant velocity joint, this portion is also quench-hardenedfor strength retention of this portion.

Moreover, of the inner peripheral face of the outer ring 16 b forconstant velocity joint, the portions of each outside engaging groove 20and the cage guide face 25 existing between each pair of thecircumferentially adjacent outside engaging grooves 20 arequench-hardened. Of these, the portion of outside engaging groove 20 arequench-hardened in order to improve the rolling fatigue life of theportion of outside engaging groove 20. Furthermore, the portion of cageguide face 25 is quench-hardened in order to improve the wear resistanceand seizure resistance of the portion of cage guide face 25 which comesrubbingly in contact with the outer peripheral face of the cage 24constituting the constant velocity joint 2 c. Consequently, the portionof the inner peripheral face of the outer ring 16 b for constantvelocity joint where the outside engaging grooves 20 and the cage guidefaces 25 are formed, is quench-hardened around the entire periphery.

On the other hand, the inner peripheral face of the hub 5 b, excludingthe portion corresponding to the engaging step portion 32 a, is notquench-hardened. In particular, the portion positioned on the innerdiameter side of the quench-hardened portion corresponding to the smalldiameter step portion 13, is not quench-hardened. In this manner,because the portion positioned on the inner diameter side of thequench-hardened portion corresponding to the small diameter step portion13 is not quench-hardened, the quench-hardened portion does notpenetrate through from the inner peripheral face of the hub 5 b to theouter peripheral face thereof. That is, because the distance between thequench-hardened portion corresponding to the small diameter step portion13 and the inner peripheral face of the hub 5 b is short (the relevantportion is thin), if the inner diameter side of this portion isquench-hardened, the quench-hardened layer at this portion may penetratethrough from the inner peripheral face of the hub 5 b to the outerperipheral face thereof. The quench-hardened layer, although beingdifficult to deform, is brittle with poor toughness, and is easilybroken due to the impact load. Therefore, it is not desirable for thequench-hardened layer to penetrate through the inner and outerperipheral faces of the hub 5 b. On the other hand, in the case of thehub 5 b constituting the wheel drive unit of the present invention, thepartial existence of brittle portions is prevented, so that it ispossible to prevent the occurrence of damage such as cracking in the hub5 b or a drop in impact resistance of the hub 5 b accompanying thequench-hardening process for the hub 5 b.

Furthermore, with respect to this hub 5 b, neither the portion forforming the crimped portion 42 a, that is, the cylindrical portionformed on the inner end of the hub 5 b, nor the portion at the tip end(the outer end) of the spline shaft 18 where the engaging groove 47 isformed, are quench-hardened. Of these, the cylindrical portion forforming the crimped portion 42 a is not quench-hardened but is left asit is so as to form a high quality crimped portion 42 a without theoccurrence of damage such as cracking in the crimped portion 42 a, whenforming the crimped portion 42 a in order to connectingly secure theinner ring 6 to the hub 5 b. Furthermore, the portion at the tip end ofthe spline shaft 18 in which the engaging groove 47 is formed is notquench-hardened but is left as it is so as to prevent damage such ascracks developing from small notches, due to heat treatment.

The wheel drive unit of the present example is formed by combining thebearing unit 3 c for wheel drive constructed as mentioned above, with adrive shaft 28, as shown in FIG. 1, and a constant velocity joint 33 ofthe tripod type, being the first constant velocity joint described inthe claims. That is, a male spline portion 29 b provided on the outerend of the drive shaft 28 is spline engaged with the second spline bore21 provided at the center of the inner ring 17 for constant velocityjoint constituting the bearing unit 3 c for wheel drive. Then, the snapring 37 stoppingly engaged in the engaging groove 30 formed around thewhole periphery of the outer peripheral face at the outer end of themale spline portion 29 b, is connected to the engaging step portion 32formed on the opening rim at the outer end of the second spline bore 21,thereby preventing the male spline portion 29 b from coming out from thesecond spline bore 21. Moreover, the inner end of the drive shaft 28 isconnectingly secured to the center of the trunnion 34 of the constantvelocity joint 33 provided on the output shaft of the differential gear.

That is, the inner end of the drive shaft 28 is connected to the centerof the trunnion 34 constituting the constant velocity joint 33 providedon the end of the output shaft of the differential gear (not shown inthe figure). Furthermore, a pair of boots 56 a and 56 b for preventinggrease leaks and preventing the ingress of foreign matter arerespectively secured between the outer peripheral faces at theintermediate portion of the drive shaft 28 and the peripheral face atthe outer end of the housing 55 constituting the constant velocity joint33 and the peripheral face at the inner end of the outer ring 16 b forconstant velocity joint. Each of these boots 56 a and 56 b is formed inan overall cylindrical shape with the intermediate portion formed in abellows shape.

According to the wheel drive unit of the present invention constructedas mentioned above, connection between the rolling bearing unit 1 c forwheel support and the constant velocity joint 2 c which constitute thewheel drive bearing unit 3 c is performed by the snap ring 31 b.Therefore, simplification of the assembly operation is devised in asimilar manner to the case of the beforementioned second example of theconventional construction shown in FIG. 7. However, according to thewheel drive unit of the present invention, because as mentioned before,each constituent element of the bearing unit 3 c for wheel drive isregulated for optimum properties, the durability of the bearing unit 3 cfor wheel drive can be ensured.

Next, FIG. 4 shows a second example of an embodiment of the presentinvention. In the case of this example, a radially wide stepped face 57is formed on an opening rim at the outer end of a spline bore 15 at anintermediate part of a hub 5 c constituting a wheel drive bearing unit 3d. This stepped face 57 corresponds to the first engaging portiondescribed in the claims. Moreover, a snap ring 31 c is provided to havethe inner periphery thereof stoppingly engaged in an engaging groove 47being the second engaging portion, formed in a tip end of a spline shaft18, and the half on the outer diameter side of the snap ring 31 c isengaged with the stepped face 57, thereby preventing the spline shaft 18from coming out from the spline bore 15.

In the case of the present example, a radially wide ring in asemi-circle annular shape with a discontinuous portion provided at onecircumferential location, is used for the snap ring 31 c. Therefore, thecontact area of the snap ring 31 c and the stepped face 57 is large sothat the contact face pressure can be reduced. Consequently, in the caseof the present example, even if this stepped face 57 is notquench-hardened in particular, plastic deformation of the stepped face57 can be prevented. The construction and operation of other parts issubstantially the same as for the case of the first example.

Next, FIG. 5 shows a third example of an embodiment of the presentinvention. This example shows the case where the present invention isapplied to the construction of the third example of the conventionalconstruction shown in FIG. 8. An outer ring 16 c for constant velocityjoint constituting a constant velocity joint 2 d, and corresponding tothe drive member described in the claims, is connected to an inner endof a hollow hub 5 d constituting a bearing unit 3 e for wheel drive, viaa spacer 38 a serving as a connecting member. The spacer 38 a may beformed separated from (FIG. 5) or integral with (FIG. 9) the inner ring6. Of the inner and outer peripheral faces of the sparer 38 a, the innerperipheral face formed with a female spline portion 39 on the innerdiameter side is quench-hardened along the entire axial length, and theouter peripheral face formed with a male spline portion 40 on the outerdiameter side corresponding to the first spline portion described in theclaims, excluding an inside engaging groove 44 corresponding to thefirst engaging portion described in the claims, is quench-hardened.Furthermore, the female spline portion 43 on the outer diameter sidecorresponding to the second spline, formed on the inner peripheral faceat the outer end of the constant velocity joint outer ring 16 ccorresponding to the drive member described in the claims, excluding anoutside engaging groove 45 corresponding to the second engaging portion,is also quench-hardened. Other than this, regarding the basicconstruction of the bearing unit 3 e for wheel drive, this is similar tothe third example of the conventional construction shown in FIG. 8, andthe quench-hardened portions and the non-quench-hardened portions aresimilar to the first and the second embodiments of the presentinvention.

In the case of working the present invention, regarding the form of eachof the female spline portion and the male spline portion formed forperforming torque transmission, various forms can be adopted. Forexample, both of the spline portions may be parallel splines constructedfrom spline teeth having axially parallel side faces, or may be taperedsplines constructed from spline teeth where each of the spline teeth hasside faces slightly inclined in mutually opposite directions withrespect to the axial direction. Moreover, these may be twisted splineswhere only the female spline portion is a parallel spline, and oppositeside faces of the spline portions constituting the male spline areslightly inclined in the same direction with respect to the axialdirection.

Furthermore, in the case of working the present invention, the portionssuch as the engaging groove formed in the member provided with the malespline is not quench-hardened, and is left as they are. That is, all orpart of the male spline portion formed in the member provided with themale spline portion, is quench-hardened, but in any case, the portionssuch the engaging groove are left as they are. On the other hand,regarding the female spline portion, it is optional as to whether or notthis is quench-hardened, and in the case where this is quench-hardened,the range over which this is quench-hardened can be freely selected.Moreover, in this case, it is possible to appropriately select whetheror not to quench-harden the connecting installation portion such as theengaging step portion provided on the inner peripheral face of themember provided with the female spline portion, where damage such ascracking due to heat treatment does not develop easily compared to theengaging groove. For example, in the case where the whole female splineportion is not quench-hardened, the engaging step portion and the likeare also not quench-hardened. Furthermore, in the case where only partof the female spline portion is quench-hardened, the engaging stepportion and the like may or may not be quench-hardened. Moreover, in thecase where the whole female spline is subjected to quench-hardeningtreatment, the engaging step portion and the like may be subjected toquench-hardening treatment, or only this engaging step portion and thelike may be not subjected to quench-hardening treatment. In each exampleof the embodiments, regarding the quench-hardening of the outer ring 4constituting the rolling bearing unit for wheel support, because this issimilar to the case of the conventional construction, diagrams andexplanation of the quench-hardened portions are omitted.

Furthermore, with regards to the surface roughness of both of the maleand female spline portions, this can be established by design, but, forexample, regarding the male spline, by making it with a rolling process,the surface roughness can be regulated to around 3.2Rmax. Furthermore,regarding the female spline portion, by making it with a broach process,the surface roughness can be regulated to around Ra 6.3.

APPLICABILITY TO THE INDUSTRY

The present invention is constructed and operates as described above,thus enabling a wheel drive unit with superior durability to be realizedat a low cost.

I claim:
 1. A vehicle wheel drive unit comprising a rolling bearing unitfor a vehicle wheel, a constant velocity joint unit and a snap ring, theconstant velocity joint unit comprising a first constant velocity jointhaving an output portion and a input portion connected to an outputportion of a differential gear, a transmission shaft having an outputend and an input end connected to the output portion of the firstconstant velocity joint, and a second constant velocity joint having anoutput portion and an input portion connected to the output end of thetransmission shaft, the rolling bearing unit for vehicle wheelcomprising an outer ring having an inner peripheral surface formed withouter ring raceways and being not rotatable during use, a hollow hubhaving an outer peripheral surface formed with a flange for supporting avehicle wheel near the outer end thereof, with a first inner ringraceway at the middle portion thereof, and with a small diameter stepportion formed near the inner end thereof, an inner ring having an outerperipheral surface formed with a second inner ring raceway and securelyfitted onto the small step portion of the hub, the hub having the innerend plastically deformed radially outward to form a crimped portion, aplurality of rolling members rotatably provided between each of theouter ring raceways and the first and second inner ring raceways, and aspacer formed separate from the inner ring and securely connected to thehub and having an inner end face and an outer peripheral surface formedwith a first spline portion therein, the second constant velocity jointcomprising a drive member having an inner peripheral surface at theouter end thereof formed with a second spline portion in splineengagement relation with the first spline portion, and an outer ringprovided at the inner end thereof, a first engagement portion comprisinga radially inner groove provided on the outer peripheral surface of thespacer, a second engagement portion comprising a radially outer grooveprovided on the inner peripheral surface at the outer end of the drivemember, the snap ring spanned between the first engagement portion andthe second engagement portion to prevent disengagement between the firstspline section and second spline section, the small diameter stepportion of the hub having a stepped face at the innermost end thereof,the inner ring having an outer end face abutted to the stepped face, onthe outer peripheral surface of the hub, at least the first inner ringraceway and the stepped face being quench-hardened, on the innerperipheral surface of the hub, at least a portion located on the innerdiameter side of the quench-hardened stepped face, and the crimpedportion being not quench-hardened, at least one of the grooves providedon the spacer and the drive member being not quench-hardened, the outerring of the second constant velocity joint being formed with outsideengagement groove portions on the inner peripheral surface thereof withcage guide portions each existing between a circumferentially adjacentpair of the outside engagement groove portions, on the inner peripheralsurface of the outer ring of the second constant velocity joint, atleast the outside engagement groove portions and the cage guide portionsbeing quench-hardened, and wherein the inner end face of the spacer isretained by the crimped portion of the hub to prevent the spacer andinner ring from coming out of the small diameter step portion, whereinthe first spline portion is a male spline portion formed on the outerperipheral surface of the spacer while the second spline portion is afemale spline portion provided on the inner peripheral surface at theouter end of the drive member formed in a generally substantiallycylindrical shape.
 2. A vehicle wheel drive unit comprising a rollingbearing unit for vehicle wheel, a constant velocity joint unit and asnap ring, the constant velocity joint unit comprising a first constantvelocity joint having an output portion and an input portion connectedto an output portion of a differential gear, a transmission shaft havingan output end and an input end connected to the output portion of thefirst constant velocity joint, and a second constant velocity jointhaving an output portion and an input portion connected to the outputend of the transmission shaft, the rolling bearing unit for vehiclewheel comprising an outer ring having an inner peripheral surface formedwith outer ring raceways and being not rotatable during use, a hollowhub having an outer peripheral surface formed with a flange forsupporting a vehicle wheel near the outer end thereof, with a firstinner ring raceway at the middle portion thereof, and with a smalldiameter step portion formed near the inner end thereof, an inner ringhaving an inner end portion and an outer peripheral surface formed witha second inner ring raceway and securely fitted onto the small diameterstep portion of the hub, the hub having the inner end plasticallydeformed radially outward to form a crimped portion to prevent the innerring from coming out of the small diameter step portion, and a pluralityof rolling members rotatably provided between each of the outer ringraceways and the first and second inner ring raceways, and the inner endportion of the inner ring having an inner end face and an outerperipheral surface formed with a first spline portion thereon, thesecond constant velocity joint comprising a drive number having an innerperipheral surface at the outer end thereof formed with a second splineportion in spline engagement relation with the first spline portion, andan outer ring provided at the inner end thereof, a first engagementportion comprising a radially inner groove provided on the outerperipheral surface of the inner end portion of the inner ring, a secondengagement portion comprising a radially outer groove provided on theinner peripheral surface at the outer end or the drive member, the snapring spanned between the first engagement portion and the secondengagement portion to prevent disengagement between the first splinesection and second spline section, the small diameter step portion ofthe hub having a topped face at the innermost end thereof, the innerring having an outer end face abutted to the stepped face on the outerperipheral surface of the hub, at least the first inner ring raceway andthe stepped face being quench-hardened, on the inner peripheral surfaceof the hub, at least a portion located on the inner diameter side of thequench-hardened stepped face, and the crimped portion being notquench-hardened, at least one of the grooves provided on the inner endportion of the inner ring and the drive member being notquench-hardened, the outer ring of the second constant velocity jointbeing formed with outside engagement groove portions on the innerperipheral surface thereof with cage guide portions each existingbetween a circumferentially adjacent pair of the outside engagementgroove portions, and on the inner peripheral surface of the outer ringof the second constant velocity joint, at least the outside engagementgroove portions and the cage guide portions being quench-hardened, andwherein the inner end face of the inner ring is retained by the crimpedportion of the hub, wherein the first spline portion is a male splineportion formed on the outer peripheral surface of the inner end of theinner ring while the second spline portion is a female spline portionprovided on the inner peripheral surface at the outer end of the drivemember formed in a generally substantially cylindrical shape.